The diffrences and inevidable.

a Main frame computer is a room sided computer that is used for big organizations that need that kind of computer power, like Airlines, banks and bog organizations. before they used to be these huge room sized computers, now there about the size of a refrigerator, because of new technology. there not that cheap though, they can cost up to 1 million dollars, there pretty sensitive because they are kept in climate controlled rooms.

A microcomputer is pretty much a PC (personal computer). A PC is the computer that the average person has. they can be desktops laptops or workstations. thought a lot of desktops can be huge, they are MUCH smaller than a main frame computer, but also have WAY less memory. there also Much MUCH cheaper, you can get a working laptop or desktop for about 400$. and can be kept anywhere in the house, not in a "climate controlled room".